Chhillar ventured into pageantry with Fashion Big Bazaar sponsored Campus Princess 2016, where she was crowned as one of the finalists from All India Institute of Medical Sciences in December 2016. It was conducted by the Miss India Organization. Thereafter, she went on to win the title of Femina Miss India Haryana in April 2017. Chhillar represented the state of Haryana in the annual Femina Miss India contest. During the competition, Chhillar was crowned Miss Photogenic, and later went on to win the main title as well, earning the right to represent India at Miss World 2017.

On 18 November 2017, Chhillar was crowned Miss World 2017 by outgoing titleholder Miss World 2016 Stephanie Del Valle from Puerto Rico in the finals in Sanya, China. She became the sixth Indian woman to win the crown, and the first since Priyanka Chopra, Miss World 2000.

As Miss World 2017, Chhillar returned to India on 26 November, where she was greeted by a large crowd. A homecoming press conference was arranged for Chhillar at St Regis Hotel, Mumbai. She was one of the celebrity speakers at the 2017 Global Entrepreneurship Summit in Hyderabad. Chhillar was announced as the brand ambassador for Anaemia Free Haryana. Her Beauty with a Purpose campaign, ‘Project Shakti’ was given government aid of ₹18 crore (approximately $2.8 million), ensuring free availability of sanitary napkins for all girls in the government schools of Haryana by Chief Minister of the state Manohar Lal Khattar. She was honoured with the Special Achievement Award at the 2017 CNN-IBN Indian of the Year Awards for winning Miss World. She was also India’s top trending personality on Google search in 2017. She received Proud Maker of India award at Six Sigma Healthcare Leadership Summit 2017 in New Delhi. She was also guest speaker at the 10th C4IO by Hewlett-Packard Enterprise at Pushkar. She made an appearance in special show Super Nights With Padman to promote her Beauty with a Purpose project on menstrual hygiene, in association with Akshay Kumar’s Pad Man (film).

As Miss India, she walked as a showstopper in the 2017 edition of Lakme Fashion Week. She has worked for fashion designers like Manish Malhotra and Sabyasachi Mukherjee. Chhillar made a debut in 2018 edition of the annual celebrity calendar by leading Indian fashion photographer, Dabboo Ratnani. She has been featured on the Indian edition covers of Cosmopolitan, Grazia, L’Officiel, Condé Nast Traveller, and Femina. During her reign as Miss World, she was featured in the Indonesian lifestyle magazine, HighEnd.

In February 2018, she started the first leg of her Beauty With A Purpose tour with Miss World 2017 continental winners – Magline Jeruto (Africa), Ha Eun Kim (Asia), Annie Evans (Oceania), Stephanie Hill (Europe), Solange Sinclair (Caribbean), Andrea Meza (Americas) and Miss World 2016 Stephanie Del Valle at the 1st global edition of ‘Feminine Hygiene Awareness’ campaign in Hyderabad in collaboration with Government of Telangana. They continued the campaign at Kolkata, where Bengal Chamber of Commerce and Industry hosted a special adda session on Feminine Hygiene in association with Miss World Beauty With a Purpose world tour team. They visited “New Light” NGO in slum area of Kolkata and also learnt to make low cost biodegradable sanitary pads at the Jute Industries Research Association. The team further worked on spreading awareness about menstruation and ensuring the availability of sanitary pads in rural areas. They joined hands with Aakar Innovations, an NGO that works on the same issue, to create more low cost, biodegradable sanitary napkins. She also visited Mumbai’s Dharavi slum for ‘Save the Girl Child’ event.

In May 2018, Chhillar reached Manila, Philippines for the press presentation and inauguration of Mister World 2019 contest which was to be venued in the Philippines. She was invited for an interview by the CNN Philippines broadcast channel. Chhillar later reached New Zealand as part of the Beauty with a Purpose campaign. Chhilar, along with the Miss World team visited the Ronald McDonald House in Auckland, and served in the charity house as volunteers. She was named as a judge for the Femina Miss India 2018 contest held on 19 June 2018. She crowned her national successor, Anukreethy Vas at the end of the event.

She then visited South Africa to take her project on menstrual hygiene forward. During the first day of the visit, she along with the Miss World team visited the Metro Radio in Johannesburg to commemorate the Nelson Mandela cenetary celebrations. As a result of Chhillar’s Beauty With A Purpose Project on feminine hygiene, machines that manufacture low cost and compostable sanitary pads were installed in Nelson Mandela’s birthplace Mvezo. The President of South Africa, Cyril Ramaphosa, led the official ceremony of unveiling the first Sanitary Pads Unit, on 18 July 2018, which marked the 100th birth anniversary of Nelson Mandela. Chhillar, along with Miss World 2014, Rolene Strauss, inaugurated the first sanitary pad manufacturing unit set up by them in South Africa. Apart from the launch of the sanitary pad unit, Mandela’s birthday was celebrated by handing out more than 200 blankets and winter hats to the elderly at the newly opened ‘Nosekeni Nongaphi Health Center’. The Miss World team also donated 100 bicycles to school children in Mvezo, Mandela’s home village.

Chhillar crowned her successor Vanessa Ponce of Mexico at the end of Miss World 2018, which took place in Sanya, China on 8 December 2018.

Chhillar has modelled for brands like Bata, Fashion Big Bazaar, Audi Q5, Cinnamon Hotel, Gio watches, and Club Factory. In April 2018, she was announced as the brand ambassador for the retail jewellery group, Malabar Gold and Diamonds. She was also signed up as the official brand ambassador for Adidas in India.

In May 2018, Chhillar joined hundreds of women in a 3 km walk through the streets of Delhi to create social awareness on the World Menstrual Hygiene Day. Supporting the Fit India Campaign, Chhillar along with the Vice President of India, Venkaiah Naidu waved the flag at the starting line to initiate the race, as thousands of cyclists made it to the streets of Delhi celebrating the World Bicycle Day. She is a strong advocate for vegetarianism and has expressed her views on the subject on various platforms.

Subsequent to her win at Miss World, Chhillar received widespread recognition and attention from the media. Chhillar was recognised for her achiements by CNN-IBN, and she was awarded at the 2017 Indian of the Year awards, by the organization. She was voted as the Most Desirable Woman of India in the 2018 internet survey conducted by Times of India. In 2019, she was named as the ‘Sexiest Vegetarian Personality’ in India, by PETA. She reacted to the award by stating, “Being a vegetarian has actually been a way of life for me. My parents were vegetarians and while they gave me a choice, I never felt like I was missing on something. I’ve always been a vegetarian and have never felt like I needed to change that.” In the annual award show organized by Lokmat newspaper, she was named as the most promising Fresh Face in the industry.